Non-reciprocal strip transmission line phase shifter



Feb. 27, 1968 R. R. JONES ETAL 3,371,293

NON-RECIPROCAL STRIP TRANSMISSION LINE PHASE SHIFTER Filed Aug. 24, 19654 Sheets-Sheet 1 QN moheifiaum OEPUNJEO music- 325: GET-2&2

INVENTORS Raymond R. Jones and Lawrence R. Whicker WITNESSES B TOEiEYFeb. 27, 1968 I R. R. JONES ETAL 3,371,293

NON-RECIPROCAL STRIP TRANSMISSION LINE PHASE SHIFTER Filed Aug. 24, 19654 Sheets-Sheet 2 FIG. 2 A'rcHme CONDUCTOR V SQUARE LOOP FERRITE p6\ '36/27 FIG. 3

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DIFFERENTIAL PHASE SHIFT (DEG/INCH) (O I I l I I l l l l l l O 5.0 5.I5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6.0

FREQUENCY (G C) woo FIG. 4

FREQUENCY (GC) FIGURE OF MERIT (LN/DB) Feb. 27, 1968 R. R. JONES ETAL3,3 93

NON-RECIPROCAL STRIP TRANSMISSION LINE PHASE SHIFTER 4 Sheets-Sheet 5Filed Aug. 24, 1965 SQUARE LOOP FERRIIE mELEc'rRK':

FIG. 6 4 50 HING l 'c UCTORS l I DIELECTRIC 6 5 r 5 1 A 5 m m I Y 2 n l2 C M E 5 m E w E R F 5 5 4 O O O O O O O O O 8 7 6 5 4 3 2 liuztmmumoue .Eim umqzm 4 .zumum. .=o

Feb. 27, 1968 R. R. JONES ETAL Filed Aug. 24, 1965 LATCHING CONDUCTORNON-RECIPROCAL STRIP TRANSMISSION LINE PHASE SHIF'TER 4 Sheets-Sheet 4 226 26 20 2L A2 I I I FIG. 8

SQUARE LOOP/ I I /FERRITES a \-MATCHING 6 I TRANSFORMER M as MATCHINGTRANSFORMER 26 4 I LATCHING cououcron FIG."

United Sttes Patent 3,371,293 NQN-RECEPROtIAL STRIP TRANSMESSEGN LINEPHASE SlallFlER Raymond E. Jones, Baltimore, and Lawrence R.

Whiclrcr, Severna Park, Md, assignors to Westinghouse ElectricCorporation, Pittsburgh, Pa, a corporation of Pennsylvania Filed Aug.24, 1965, Ser. No. 482,074 1 Claim. (til. 333-24.]L)

ABSTRACT OF DISCLQSURE A strip transmission line phase shiftercontaining therein at least one ferrite, each ferrite being of a closedloop geometry. One wall of each ferrite is positioned immediatelyadjacent the center strip conductor and provides dielectric loading todistort the uniform transverse field for obtaining the planes ofcircular polarization. In such a manner the dielectric properties aswell as the magnetic properties of the ferrite are used.

The present invention relates generally to microwave phase shifters andmore particularly relates to a nonreciprocal strip transmission linephase shifter.

Electronically controlled phase shifters capable of being switched insub-microsecond intervals are highly desirable, for example, in thefield of phased antenna arrays. However, the large number of necessaryphase shifters presents a matrix which adds considerable size and Weightto a radar system. Strip transmission line components are attractivelycompact but their utilization for phase shifting has required largesolenoids or magnets external to the strip line to xagnetize ferriteslugs located within the line.

It is well known that circularly polarized magnetic fields are anecessary requirement for the operation of nonreciprocal striptransmission lines. A dielectric material is generally disposed withinthe transmission line to asymmetrically load the line to distort theuniform transverse electric field. The distortion occurs in the form ofa density gradient in the transverse electric field, which gives rise toa longitudinal magnetic field component. When a transversely magnetizedferrite is placed in this region of circular RF magnetic field,non-reciprocal phase shift is obtained.

Briefly, the present invention disposes a plurality of ferrite elementsbetween the ground planes, of a strip transmission line structure. Eachferrite element provides dielectric loading and is positioned toasymmetrically load the line to produce the necessary longitudinalmagnetic field component for circular polarization. The elements arechosen to be of diiferent lengths. Each is provided with a separate.current path extending therethrough for imposing a circular magneticfield to selected elements for causing the elements so energized toassume one of two stable remanent magnetization states. The closedmagnetic loop associated with each element is located entirely withinthe strip line structure. The magnetic loop is disposed transverse tothe longitudinal magnetic field component to shift the phase of theenergy in accordance with the length of the elements latched.

Accordingly, an object of the present invention is to provide anon-reciprocal strip transmission line phase shifter which has thedesired qualities associated with strip transmission linecomponents andexhibits digital phase shift characteristics.

Another object of the present invention is to provide a non-reciprocalstrip transmission line phase shifter which is compact and light inweight yet capable of digital phase shifting in sub-microsecondintervals;

Another object of the present invention is to provide a non-reciprocal,digital phase shifter which combines the rapid switching speeds offeredby latching devices and the compactness of a strip transmission linestructure.

Another object of the present invention is to provide a phase shifterwhich is much smaller than its waveguide counterpart, and is bettersuited for integration into a compact matrix which may contain manyidentical phase shifters.

Another object of the present invention is to provide strip transmissionline phase shifters which are of compact geometry, provide good figuresof merit, and require low driving power.

Further objects and advantages of the present invention will be readilyapparent from the following detailed description taken in conjunctionwith the drawing, in which:

FIGURE 1 is a perspective view, partly in section, of a preferredembodiment of the present invention;

FIG. 2 is a cross-sectional view taken along the line indicated by thearrows Il-ll of the illustrative embodiment shown in FIG. 1;

FIGS. 3 and 4 are graphical representations of characteristic curvesshowing the operation of the illustrative embodiment of FIG. 1;

FIG. 5 is a partial cross-sectional view of an alternate embodiment ofthe present invention;

FIG. 6 is a partial sectional view of another alternate embodiment ofthe present invention;

FIG. 7 is a graphical representation of characteristic operating curvesfor the illustrative embodiment shown in FIG. 6;

FIGS. 8, 9 and 10 are top, side and end views of still anotherillustrative embodiment of the present invention; and

FIG. 11 is a partial cross-sectional view of yet another illustrativeembodiment of the present invention.

A five bit strip transmission line phase shifter illustrated in FIG. 1,including ground planes 2 and 4 with a center strip conductor 6longitudinally disposed thereinbetween and terminated at one end at aninput connection 8 and at the opposite end an output connection 10.Ferrite elements l2, l4, 16, 18 and 2d of different lengths arelongitudinally disposed adjacent an edge of the center strip conductor6. Quarter wave dielectric matching transformers 22 are used at the endsof the ferrite structure. Dielectric separators 24. having the samepermittivity as the ferrite elements are used to isolate the variousferrite bits. A latching conductor 25 (FIG. 2) extends longitudinallythrough the ferrite elements, with-latching control wires 26 connectedto the latching conductor 25 through the dielectric separators 24. Abrace 27 supports each control wire 26 entering each separator 24;. Whendesired, separate latching conductors may be provided through eachelement. Selected ferrite elements are magnetized in a predetermineddirection as determined by signal current pulses passing through theferrite element when their respective latching control wires 26 areenergized.

it is well known that circularly polarized magnetic fields are anecessary requirement for the operation of non-reciprocal waveguidedevices. However, no component of circular polarization exists in astrip transmission line for the dominant TEM mode. The TEM mode isunsuitable for non-reciprocal phase shift unless the mode can bedistorted to create the required circular polarization. In accordancewith the present invention the ferrite elements 12 through 2%, of achosen dielectric constant, asymmetrically load the transmission line todistort the uniform transverse electric field. This distortion occurs inthe form of a density gradient in the transverse electric field, whichgives rise to a longitudinal magnetic field component near theair-dielectric interface. At the same time, the ferrite elements whenlatched to a remanent state provide a magnetization component transverseor perpendicular to the longitudinal component in the region of thecircular RF magnetic field to obtain non-reciprocal phase shift of themicrowave energy traveling through the strip transmission line.

Specifically referring to FIG. 2, the ferrite element 12 includes a topwall 30, a bottom wall 32 and side walls 34 and 36 disposed to form alongitudinal bore or aperture 38 through which the latching conductor 25is threaded. The ferrite element 12 is positioned with its side walls 34adjacent one edge of the center conductor 6 by means of foam supports40. The necessary transverse magnetic field for non-reciprocal phaseshift is provided by the side wall 34 when the ferrite element 12. islatched or switched to a predetermined state of remanent magnetization.The opposite wall 36, top wall 30 and bottom wall 32 complete themagnetic path and provide the necessary dielectric loading to obtain theE field gradient atthe interface between the wall 34 and free space.

Each ferrite element is chosen to have a square loop magnetization curvein which the remanent magnetization M is almost equal to the saturationmagnetization M The side wall 34 of the ferrite element selected toprovide transverse magnetic field is magnetized in a chosen direction bypassing a current therethrough by means of the latching conductor 25.For example, a positive current pulse through that portion of thelatching conductor 25 associated with the selected ferrite element willprovide a magnetic field in a circumferential direction to saturate theferrite element in, say, the plus direction, M The ferrite element willretain the larger part of its magnetization when the current pulse isremoved and assume a positive or first state of remanent magnetization MThe selected ferrite element is then set to be latched at its positiveremanent magnetization point, +M However, if a negative current pulse isapplied, the magnetization will be reversed and the material will remainset at a negative or second state of r-emanent magnetization, -M',.

The side wall 34 adjacent the edge of the center conductor 6 willstrongly interact with the microwave energy and differentially shift thephase thereof when the direction of the magnetic field in the side wall34 is changed. The distance across the ferrite element to the other sidewall 36 is made sufiiciently large so that the microwave energyinteraction with the opposite side wall 36 is insignificant in the phaseshifting of the microwave energy. The ferrite elements are of varyinglength to shift the phase of the microwave energy in different discretesteps, the amount of ferrite material, when magnetized, determining thenumber of degrees phase shift that will occur.

Measured phase shift and merit data for the illustrative embodimentshown in FIG. 2 is illustrated in FIGS. 3 and 4. The operating curve Aresulted from the use of ferrite material having a 47TM5 of 1700 gaussfor the latching elements 12 through 20. The characteristic curve Bresulted from the use of yttrium iron garnet with a 471-M of 1600 gaussfor the latching elements 12 through 20. It is seen that in excess of100 degrees of phase shift per inch is obtained from both materials.This is considerably more than has been obtained for waveguideconfigurations. A figure of merit, which is defined as degrees of phaseshift for db of loss, is shown by the characteristic curve C and is inexcess of 400 for both materials across a 5% frequency band.

When desired, additional dielectric material 42 in FIG. 5 may bedisposed between the center conductor 6 and the ground planes 2 and 4 tofurther asymmetrically load the strip line and provide the desiredelectric field density gradient. The addition of such additionaldielectric material however, has been found not to improve theperformance significantly.

The alternate embodiment of FIG. 6 utilizes stacked ferrite elements 50and 52 disposed between the center conductor 6 and the ground plane 2and ground plane 4, respectively. The side wall of interest ismagnetized in the same direction for interaction with the circularmagnetization. Separate latching conductors 54 and 56 are simultaneouslyenergized by a proper pulsing circuit to shift the phase of themicrowave energy. When desired, additional dielectric loading may beprovided by the insertion of dielectric material 58 extendinglongitudinally within the aperture of each of the latching elements 50and 52. With the arrangement of FIG. 6, considerably less phase shiftwill be obtained; and the obtained differential phase shift is highlydependent on the dielectric loading within the elements 50 and 52. Plotsof phase shift using dielectric materials of various constants are shownin FIG. 7. Although considerably less phase shift is obtained for agiven volume'of ferrite material, the geometry shown in FIG. 6 is usefulfor high power application where reduced interaction with the microwaveenergy is required.

FIGS. 8, 9 and 10 illustrate an alternate configuration wherein theferrite elements are alternately disposed on opposite edges of thecenter strip conductor 6. In such a manner the ferrite elements can bestacked to provide a more compact latching ferrite strip line phaseshifter.

A printed circuit strip transmission line phase shifter is illustratedin FIG. 11 wherein the center conductor 60 is printed on clad lowdielectric constant material 62 disposed between ground planes 64 and66. Sufficient dielectric is removed to allow for the inclusion of theferrite latching element 68 and its associated latching conductor 70 andlatching controlled wires 72.

Hence, it is readily apparent that the present invention combinesferrite latching elements and the strip transmission line to obtain thedesirable characteristics of both. The configuration of ferrite latchingelements and their disposition within the strip transmission line aboutthe center strip conductor satisfies the circular field requirements fornon-reciprocal action and at the same time maintain a closed pathgeometry for the magnetic circuit.

The latching elements have been referred to as ferrite elements but itis to be understood that the latching elements may be of any suitablematerial such as, for example, spinel-type materials and garnet-typeferrites which contain rare earths. It is to be understood that allsuitable materials including ferri-magnetic or gyromagnetic materialsmay be utilized to provide the latching function necessary for providingthe transverse magnetic field while being capable of switching insubmicrosecond intervals.

Experimental verification of differential phase shift has been obtainedat C-band frequencies. The phase shift was measured at 112 and theinsertion loss at .25 dbs, respectively. This yields a figure of meritof approximately 450 per db, at 5650 megacycles.

While the present invention has been described with a degree ofparticularity for the purposes of illustration, it is to be understoodthat all modifications, alterations and substitutions within the spiritand scope of the present invention are herein meant to be included.

We claim as our invention:

1. A multiple bit latching ferrite-strip line phase shifter comprising,in combination; a center strip conductor longitudinally disposed betweenground planes; a plurality of ferrite elements each of different lengthand each having an aperture extending therethrough; said ferriteelements disposed end to end longitudinally adjacent an edge of saidcenter strip conductor; a wall portion of each said ferrite elementabutting the edge of said center strip conductor; said ferrite elementshaving a dielectric constant substantially greater than air; signalmeans threaded through the aperture of each said ferrite element forindividually latching its respective 5 6 adjacent wall in apredetermined state of remanent mag- References Cited netization; theremaining portion of said ferrite ele- UNITED STATES PATENTS mentproviding a closed magnetic loop with said wall portion located entirelywithin the space between the ground $6,23

planes; said ferrite elements longitudinally disposed along 5 saidcenter strip conductor being alternately disposed HERMAN KARL SAALBACH,'y Examlneron opposite edges of said center strip conductor. P. L.GENSLER, Assistant Examiner.

